Polyethylene terephthalate (also referred to as “PET”) is a polyester of terephthalic acid and ethylene glycol and can be obtained by the polycondensation of dimethyl terephthalate with ethylene glycol, and also terephthalic acid with ethylene glycol or ethylene oxide. PET exists both as an amorphous (transparent) and as a semi-crystalline (opaque and white) thermoplastic material. Generally, it has useful chemical resistance for mineral oils, solvents and acids but not to bases. Semi-crystalline PET has good strength, ductility, stiffness and hardness. Amorphous PET has better ductility but less stiffness and hardness. PET is used to make bottles for soft drinks, fibers for a variety of applications and other household and consumer products.
Unfortunately, despite recycling efforts, billions of pounds of PET still become solid wastes that are dumped into landfills or incinerated annually all over the world. The substantial amount of PET that is disposed into landfills creates significant waste. The incineration of PET destroys a material made from non-renewable hydrocarbon resources that could be used more effectively.
Polytrimethylene terephthalate (also referred to as “PTT” herein) is known to be useful as an engineering thermoplastic for injection molding applications, as described in U.S. Pat. No. 5,326,806. In general, PTT is prepared by reacting, at elevated temperature, a molar excess of 1,3-propanediol with terephthalic acid in a multi-stage (esterification/polycondensation) process, with removal of by-product water, for a time effective to produce polytrimethylene terephthalate. The polymerization conditions are selected so as to produce molten polyester having a target intrinsic viscosity of at least about 0.4 dl/g, preferably about 0.4 to about 1.0 dl/g. Polytrimethylene terephthalate may also be produced by the reaction of 1,3-propanediol with dimethyl terephthalate.
Unfortunately, conventional processes for preparing PTT do not meet the long felt need of reducing the amount of PET scrap that is ordinarily incinerated or buried in landfills. Preparing PTT from monomers requires a substantial amount of energy and it would be desired to develop novel processes for making PTT from non-monomeric sources. It would also be useful to develop a modified PTT random copolymer from PET, instead of monomers, that exhibited comparable performance properties as monomer-derived PTT.
For the foregoing reasons, there is a need to develop improved processes for making polytrimethylene terephthalate from PET, instead of monomers.
For the foregoing reasons, there is a need to develop new materials having performance properties similar to monomer-based polytrimethylene terephthalate, but that are derived from PET.